This snippet gives you all entity_id’s of all Root-IDs of the Magento instance: /** * @return array Root-IDs of all stores */ public function getAllRootIds(){# $aRootIds = array(); $aRootIds[Mage_Catalog_Model_Category::TREE_ROOT_ID] = Mage_Catalog_Model_Category::TREE_ROOT_ID; $aAllStores = Mage::app()->getStores(); foreach ($aAllStores as $iID => $store){ $rootID = $store->getRootCategoryId(); $aRootIds[$rootID]=$rootID; } return array_keys($aRootIds); }